Chinese President Hu Jintao and U.S. President George W. Bush were beaming in baby blue; the women leaders posed in peony pink.

When the debates on the future of the world trading system and other momentous issues are finished, once all the diplomacy is over, Pacific Rim leaders face one final, inescapable task during their annual summit — the donning of the host country’s costume.

Leaders at the Asia-Pacific Economic Cooperation summit in Hanoi on Sunday were invited to slip traditional Vietnamese “ao dai” silk tunics over their Western-style suits for their annual group photo — by far the most colorful ritual on their agenda.

What an ice breaker.

The normally dour and somber-faced Hu was positively beaming as he stood for the group photos. Russian President Vladimir Putin joked cordially with Bush. The wide pink turbans worn by the three women leaders gave diminutive Philippine President Gloria Macapagal Arroyo a few extra inches of height.

The custom-tailored ankle-length ao dai, pronounced “ow zai,” usually has a snug fit that is said to “reveal everything but show nothing.”

But the costumes worn by the leaders appeared designed not to reveal much of anything at all. Fashioned by famous Vietnamese designer Minh Hanh, they afforded the leaders — most of whom have ample girths — a fairly comfortable fit.

Sky blue was the most popular color among the men, with a smattering of reds, greens and yellows for a diplomatic rainbow effect.

The traditional ao dai includes a long tunic with slits up the sides revealing just an inch or so of flesh at the waist above long white slacks. The tunics the leaders wore Sunday had less revealing slits, and most wore dark slacks.

The tradition of posing in clothing symbolic of the host country began when the leaders wore leather bomber jackets at their first APEC summit in Seattle in 1993.

The centuries-old ao dai was banned briefly after Vietnam’s communist revolution but is now worn by school girls — preserving a touch of traditional elegance in a fast-modernizing society. It is rarely worn except as uniforms or for special occasions.

Over the years, the leaders have posed in Indonesian batik, Filipino barong made of pineapple fiber, and gold-embroidered Chinese silk tunics.

At times, they’ve appeared visibly ill-at-ease in the colorful and unfamiliar costumes, though in Hanoi most seemed amused by the spectacle of 21 leaders clad in gold-embossed silk.

Once they headed outdoors for the group photos in a sunny lakeside flower garden, things got a bit less comfortable, said Canadian Prime Minister Stephen Harper.